In the presence of an electric field, the dielectric constant of a semiconductor exhibits Franz–Keldysh oscillations (FKO), which can be detected by modulated reflectance. Although it could be a powerful and simple method to study the electric fields/charge distributions in various semiconductorstructures, in the past it has proven to be more complex. This is due to nonuniform fields and impurity induced broadening, which reduce the number of detectible Franz–Keldysh oscillations, and introduce uncertainties into the measurement. In 1989, a new structure, surface–undoped–doped (s‐i‐n+/s‐i‐p+) was developed, which allows the observation of a large number of FKOs and, hence, permitting accurate determination of electric fields. We present a review of the work on measuringelectric fields in semiconductors with a particular emphasis on microstructures using the specialized layer sequence. We first discuss the general theory of modulation techniques dwelling on the approximations and their relevance. The case of uniform field, obtained with this specialized structure as well as that of the nonuniform field, are addressed. The various experimental techniques are also briefly reviewed. We then summarize the various experimental results obtained in the last few years using these special structures and FKOs and find that, even in this short period, good use has been made of the technique and the structure. This is followed by a brief review of the work on nonuniform fields. In this case, the work on actual device structures has significant technological implications. Important issues such as metallization and processing, the effects of surface treatment and thermal annealing, Schottky barrier heights of different metals, piezoelectric fields in (111) grown strained InGaAs/GaAs quantum wells, and Fermi level in low‐temperature grownGaAs have been studied using this structure. This structure has also been used to study the dynamics of photomodulation, revealing the nature of the cw photoreflectance.

We present a numerical technique for open‐boundary quantum transmission problems which yields, as the direct solutions of appropriate eigenvalue problems, the energies of (i) quasi‐bound states and transmission poles, (ii) transmission ones, and (iii) transmission zeros. The eigenvalue problem results from reducing the inhomogeneous transmission problem to a homogeneous problem by forcing the in‐coming source term to zero. This homogeneous problem can be transformed to a standard linear eigenvalue problem. By treating either the transmission amplitude t(E) or the reflection amplitude r(E) as the known source term, this method also can be used to calculate the positions of transmission zeros and ones. We demonstrate the utility of this technique with several examples, such as single‐ and double‐barrier resonant tunneling and quantum waveguide systems, including t‐stubs and loops.

Optical excitation of half‐leaky guided modes has been used to determine the refractive indices of a ferroelectric liquid crystal (Merck‐SCE13) in a homeotropically aligned state. The uniform homeotropic alignment is realized, with no surface treatment, by the application of an in‐plane dcelectric field. This applied field, of the order of 5×105 V m−1 is sufficient to fully unwind the S*c helix giving a uniformly tilted homeotropic monodomain for optical characterization. Analytic and numerical modeling results indicate that, for a slab with its optic axis tilted in a plane orthogonal to the plane of incidence, two distinct critical angles appear in the half‐leaky guided mode response. These independently relate simply to the ordinary and extraordinary refractive indices of the S*c material. By fitting theoretical angle dependent reflectivities to those recorded experimentally the two refractive indices have been obtained for a range of temperatures in both the S*c and SA phases.

A method to fabricate chromium‐doped lithium niobate substrates in which the active ions are introduced by thermal diffusion from a film is reported. Chromium concentration depth profiles have been obtained by secondary‐ion‐mass spectrometry and the relevant diffusion parameters have been derived. Fluorescencespectrum and upper laser level lifetime of chromium diffused proton‐exchanged and chromium/titanium‐diffused lithium niobate waveguides have been measured. A simple model has been used to estimate the performance of such structures as waveguide optical amplifiers and lasers.

The Raman effect in semiconductorwaveguides below half‐gap is studied both experimentally and numerically. We report the depolarized Raman gain spectra up to 300 cm−1 in Al0.24Ga0.76As at pump wavelengths of 0.515 and 1.55 μm from the measurement of the absolute Raman scattering cross sections using GaAs as a reference scatterer. In addition, the coupled propagation equations for the AlGaAswaveguides are modified to include the Raman effect. By solving the coupled propagation equations numerically, we verify that the energy transfer between two orthogonally polarized pulses demonstrated in previous pump‐probe experiments [M. N. Islam etal., J. Appl. Phys. 71, 1927 (1992)] is caused by Raman effect. We also show numerically that the Raman effect induces spectral distortions on the pulses, and the energy transfer is inversely proportional to the pulse widths. The energy transfer results in a severe cross‐talk problem for sub‐picosecond pulses in AlGaAswaveguides. For example, the energy exchange is about 30% for 300 fs pulses under π phase shift conditions. Therefore, the Raman effect limits the performance of semiconductorwaveguides in optical switching applications for sub‐picosecond pulses.

We study by photoacoustic spectroscopy the band‐gap shift effect of CdSfilms. The CdSfilms were grown by chemical bath deposition and exposed to different annealing atmospheres over a range of temperature in which the sample structure changes. We show the band‐gap evolution and resistivity as a function of temperature of thermal annealing and determine the process that produces the best combination of high band‐gap energy and low resistivity.

Theoretical and experimental possibilities are presented of a modulated photothermal method, laser‐induced photoreflectance, for inspectingthermal diffusivities and quality of interfaces in composite materials with micron‐scale spatial resolutions. The models are established for semi‐infinite materials containing interfaces parallel or perpendicular to the sample surface. The applications concern thermal diffusivity measurements of anisotropicpolycrystals and detection of thermal resistance in damaged materials and at interfaces between reinforcements and matrix in composites.

We describe methods for automating the control and tracking of states within or near a chaotic attractor. The methods are applied in a simulation using a recently developed model of thermal pulse combustion as the dynamical system. The controlled state is automatically tracked while a parameter is slowly changed well beyond the usual flame‐out point where the chaotic attractor ceases to exist because of boundary crisis. A learning strategy based on simple neural networks is applied to map‐based proportional feedback control algorithms both with and without a recursive term. Adaptive recursive proportional feedback is found to track farther beyond the crisis (flame‐out) boundary than does the adaptive non‐recursive map‐based control. We also found that a continuous‐time feedback proportional to the derivative of a system variable will stabilize and track an unstable fixed point near the chaotic attractor. The positive results suggest that a pulse combustor, and other nonlinear systems, may be suitably controlled to reduce undesirable cyclic variability and extend their useful operating range.

A self‐consistent hybrid Monte Carlo‐fluid model for a direct currentglow discharge is presented. The Monte Carlo part simulates the fast electrons while the fluid part describes the ions and slow electrons. Typical results of the model include collision rates of the fast electrons, energy distributions of these electrons, fluxes and densities of the different plasma species, the electric field and the potential distribution, all as a function of position from the cathode. The influence of the negative glow on the calculations in the cathode dark space is studied. Moreover the influence of three‐dimensional scattering instead of forward scattering and the incorporation of side wall effects is investigated. Calculations are carried out for a range of voltages and pressures in order to study their influence on the calculated quantities. Comparison was made between total electrical currents calculated in the model and experimentally measured ones to check the validity of the model.

Nanometer‐thick hydrocarbon films were plasma polymerized in a rf pulse discharge in an acetylene/argon mixture and were mechanically patterned by the AFM(atomic force microscope). In addition a dc bias voltage was applied to the goldcoated Si3N4AFM tip. Depending on the experimental conditions, different patterns have been observed: mechanical indentation, electric charge, and material deposition. The viscous properties of the plasmadepositedfilm affects the movement of the AFM tip while it is scanning the surface in a contact mode, and also affects the size and shape of the patterned area. Spikes of about 25–72 nm height and 60–200 nm width were formed from gold transferred from the newly mounted goldcoated tips. The mechanism of golddeposition could be assigned to the Joule heating of the tip, resulting from the electric breakdown of underlying dielectric layers.

It is shown experimentally that the electron charge emitted from triglycine sulfate pulse ferroelectric cathodes can be as large as 129 μC/cm2. This charge considerably exceeds the measured value of spontaneous polarization,Ps=2.8 μC/cm2. A bipolar voltage is found to facilitate the appearance of the electron emission. It is proposed that the source of the emission current is the plasma of uncompleted surface discharges. This plasma is initiated at the metal‐vacuum‐dielectric triple points both by the field electron emission and the electron emission stimulated by polarization switching.

This work studies the dynamics of melting in current‐carrying conductors. Formulae are derived which describe the dependence of temperature at the front of phase transition upon the distance from the axis of the conductor. The thermodynamic stability of a phase transition front is investigated. It is shown that due to strong variations of conductivity during melting the rate of change of conductivity is of the same order as an active resistance of a conductor. Clearly the magnitude of this effect depends upon the ratio of electric conductivities in liquid and solid phases. The effect is stronger when this ratio is lower.

The Phillips Laboratory working fluid experiment is a research effort to study the compression of a hot hydrogen gas using an electromagnetically imploded solid liner. In our experiments, the solid liner is driven by a 5 MJ discharge which Joule heats the aluminum, melting and eventually vaporizing it. This numerical study explores the vaporization and flux penetration of a solidaluminum liner during its implosion. In particular, it considers the effect that flux which has penetrated the liner has on the hot hydrogen working fluid. A study of the dynamics of the solid liner was performed with one‐dimensional radiationmagnetohydrodynamic simulations, which included a careful treatment of the electrical resistivity near the phase transitions. An analytic snowplow model is developed in order to estimate the minimum working fluid density required to ignore flux penetration through the liner.

A plasma chemistry model is presented that explains the observed CO2dissociation levels in a closed‐cycle fast‐axial‐flow CO2 laser. The model includes reactions between the neutral species CO2, CO, O, O2, O3, H2O, and OH, and the negative ions O−, O−2, CO−3, and CO−4. Dissociation rates are computed by solving the electron Boltzmann equation for experimental values of the reduced field E/N. It is found that gas replenishment and the neutral recombination reaction between CO and the OH radical are the most effective mechanisms to suppress the CO concentration in the gas circuit. The influence of CO2dissociation on the laser output power level is discussed.

A particle‐in‐cell (PIC) simulation of an axisymmetric electron‐cyclotron‐resonance (ECR) etching tool is developed in which up to 2×106 particles per species are loaded in a two‐dimensional spatial computational mesh (r,z), along with three velocity components (vr,vθ,vz). An ECR heating scheme based on single‐particle trajectories in the resonance zone generates the simulated plasma. Electron‐ and ion‐neutral elastic and inelastic collisions are treated by a null Monte Carlocollision method. The code generates the electron and ion‐velocity distributions, plasma potentials, and densities in a CF+3/CF4etchingplasma. In addition, a novel scaling technique which bridges the gap between the ion and electron‐time scales and accelerates the rate of convergence of the code is introduced for a PIC code. The predictions of the code show that microwaves are completely absorbed before reaching the exact location of resonance.

The most important forces that influence the motion of particles in a glow discharge plasma are the electrostatic force, the ion drag force, the neutral drag force, thermophoresis, and gravity. In this article we present a transport model that predicts the distribution of particles in plasma reactors in terms of the fundamental forces that act on the particles. We compare the model predictions to experimental measurements of particle distributions in a rf parallel plate plasma reactor.

Based on the analysis of the micro‐processes due to the interaction of synchrotron radiation with materials, we have developed a theoretical method to calculate the heat energy deposited when synchrotron radiation passes through insert devices (filters, mirrors or monochromators). The micro‐processes are photoionization,Compton scattering,Rayleigh scattering, electron elastic and inelastic collisions, electron Bremsstrahlung scattering and the Auger process. The energy of x rays is converted into the electrons’ kinetic energy and atomic excitation energy by photoionization and Compton scattering. High‐energy photoelectrons slow down mainly through inelastic collisions with the atoms in materials. The energy deposition in a material is simulated according to the x‐ray atom interaction cross sections and photoelectron‐atom collision cross sections. The results of a calculation for x rays traversing Si and Be plates of 1.0 cm in thickness are presented and discussed as one typical example concerning important materials in optical devices. The dependence of the energy deposition on the angle of incidence of the x rays is also discussed. Both the utility and validity of the present simulation method are discussed.

A borondoped epilayer was used to investigate the interaction between end of range dislocation loops (formed from Ge+ implantation) and excess point defects generated from a low dose 1014/cm2 B+ implant into silicon. The borondoping spike was grown in by chemical vapor deposition at a depth of 8000 Å below the surface. The intrinsic diffusivity of the boron in the doped epilayer was determined by simply annealing the as‐grown layer. The end of range (type II) dislocation loops were created using two overlapping room‐temperature Ge+ implants of 75 and 190 keV each at a dose of 1×1015/cm2. Upon annealing the amorphous layer regrew and a layer of type II dislocation loops formed ∼2300 Å deep at a density of ∼8×1010/cm2. The enhancement in the buried boron layer diffusivity due to the type II loop forming Ge+ implant was observed to increase approximately between 2.5 and 5 min from 1500× to a value 2500× above the intrinsic diffusivity before dropping back to intrinsic levels after 30 min at 800 °C. A low‐energy (8 keV) 1×1014/cm2 B+ (Rp=320 Å) implant into material without loops resulted in an average enhancement of 1540× in boron epilayer diffusivity after 2.5 min at 800 °C. The enhancement dropped down to intrinsic diffusivity levels after 5 min at 800 °C. When a layer of loops was introduced and annealed prior to and deeper than a subsequent low‐energy B+ implant, annealing of the B+ implant produced no measurable enhancement in the buried B layer diffusivity. Taken together this imples that the interaction kinetics between the dislocation loop layer and the damage induced interstitials are primarily diffusion limited and the loops are absorbing a significant fraction of the interstitials produced by the low‐energy B+ implant.

Antimony/aluminium films in bilayer and multilayer geometries were irradiated at liquid‐nitrogen temperature with 50–900 keV ion beams ranging in mass from 20Ne to 208Pb. Depth profiling of the element concentrations was carried out via Rutherford backscattering spectroscopy. The formation of intermetallic phases and phase segregation was analyzed by means of x‐ray diffraction, cross‐section transmission electron microscopy, and scanning electron microscopy. From the low‐dose irradiation data, the mixing rates k were obtained and found to depend linearly on the energy density FD deposited at the interface. The mixing efficiency of Sb/Al bilayers, k/FD=296(30) Å5/eV, supports the local thermal spike model. After high‐fluence irradiations of Sb/Al bilayers with 550 keV Xe++ ions, a reacted layer of crystalline SbAl (B3 phase) at the interface was observed. Sb/Al multilayersirradiated with 900 keV Xe++ ions were found to become amorphous. Phase formation was studied as a function of the ion fluence, irradiation energy, and ion mass, and was found to start at that fluence, where cracking and shrinking of the Sb top layer and an increase of the sputtering yield were also observed.

The sensitivity to x‐ray beam energy of structure measurements using x‐ray standing waves (XSW) generated under conditions of total external reflection has been determined. To this end, the optical properties of the system were examined in a theoretical analysis to identify possible energy‐dependent components such as surface roughness. The analysis shows that, provided surface roughness is small (Debye–Waller factor less than 10 Å) and the energy range covered in the XSW measurements lies within several keV, its contribution can be accounted for satisfactorily by a simple Debye–Waller factor. In addition, a series of XSW measurements were made on Langmuir–Blodgett films of manganese arachidate (C20:0) on a goldmirrorsurface at three incident x‐ray beam energies in the 7–11.2 keV range. The XSW data were analyzed to account for the Debye–Waller factor. No obvious dependence on incident x‐ray energy was found. These results demonstrate that the contribution of surface roughness to the x‐ray fluorescence yield profile is minimal under these conditions. Thus, mirrors of the type and quality used in these experiments are useful in XSW measurements where multiple element types are incorporated as structural labels in organic thin films and at surfaces. We also demonstrate that the resolving power of the XSW method is sufficient to distinguish and to locate two separate probe atom layers in a single Langmuir–Blodgett film.